Somewhat on topic, Perl 5.8 is not 64-bit safe! You think you're all fine with a 64 bit number encoded as a string, then you try to do math on it and you're screwed. A friend of mine threw together a 64 bit math library using bit arrays, but it is painfully slow when trying to do real work.

Math::BigInt is a step in the right direction, but I think it's useless when you're trying to do math on hex input to produce hex output.